The role of inter-state Renner-Teller coupling in the dissociation of triatomic molecules

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Abstract
An evolving wavepacket study has been made of the rate of radiationless transition from a linear excited electronic state of a triatomic molecule to a lower dissociative bent state, brought about by vibronic interaction (the Renner-Teller effect) where both states correlate with a Π state in the linear configuration. The rate is found to increase (i) with decrease in the quantum number π2 of the upper state bending vibration, (ii) with increase in the quantum number K for the axial component of the total rotational angular momentum, and (iii) with increase in the divergence between the two Born-Oppenheimer potential curves upon bending. There is a maximum crossing probability of 50 per cent during one half-period of the bending vibration. The model is validated by calculating the rate of dissociation of HCO ⪷A 2 A″ → H + CO, giving close agreement with experiment. It is then applied in a discussion of the dissociation pathways for the [Btilde] 1 A 1 state of H2O, providing an explanation for the low quantum yield of OH in its A 2Σ+ state (+ H) even though these states are adiabatically correlated.